Are you wanting to create the effect in Photoshop? If so, it's mainly just a simple pattern overlay using a dot pattern.
Here's one thread on the matter:
https://www.photoshopgurus.com/forum/photoshop-newbies/48427-dot-layer-image.html
I wasn't around when that thread came about and only got to view it much later.
@
Dan75 ...
The "noise" was actually generated by a weeeeeee png image viewable if you right click on the images and select View Background..... it's really tiny.....
Here and in Sam's linked thread, it's correctly said and defined as a
Wordpress Theme option that's either a
plugin or widget and that everyone's reproductions in the other thread are spot-on.
Here's my take on it using the actual 2x2 pixel image which I first saved in PSD format and used to Define Pattern fill..... The faint dot (or square pixel, whatever it is) is on the upper left hand quarter canvas side of home-bg.psd (zoomed to max).
If anyone's interested.... here's that png..... hope you guys can find, click and download that miniscule spec of an amoeba enclosed in parenthesis.....
(
)
It's there. Just hover your mouse pointer over the area to detect it.....